Hydraulic power circuit affording parallel regeneration paths



0. L. RICE Nov. 11, 1969 HYDRAULIC POWER CIRCUIT AFFORDING PARALLEL REGENERATION PATHS Filed May 17, 1968 INVENTOR ORVAL L..R|CE

ATTORNEY United States Patent US. Cl. 91-438 4 Claims ABSTRACT OF THE DISCLOSURE A hydraulic power circuit for actuating a component and for effecting rapid and controlled movement of the component under the action of external loads. The circuit is characterized in that it provides a pair of parallel regeneration paths through which oil can be simultaneously transferred from the contracting to the expanding ends of the actuating cylinders. One path extends through and is 'throttled selectively by a directional control valve, and the second is throttled by a separate by-pass valve which is located at or near the cylinders and is controlled so as to limit the rate of flow through the first path. A bleed connection containing a fixed orifice permits oil displaced by the rods of differential area cylinders to escape from the first path to a tank.

BACKGROUND OF THE INVENTION Many hydraulic power circuits are used today to actuate'components subject to large, unidirectional, external loads, usually gravitational loads. A good example is the lift circuit employed on earth-moving loaders. In this circuit, the bucket-carrying boom commonly is positioned by a pair of parallel-connected double-acting piston motors, hereinafter called cylinders, of the difierential area type which are installed in such manner that the load imposedby the boom tends to contract their head ends. The cylinders are controlled by a directional control valve which affords the following positions: a neutral or hold position in which the cylinders are hydraulically locked, a raise position in which the head and rod ends of the cylinders are connected with a supply pump and tank, respectively, a power down position in which the connections between the cylinders and the pump and tank are reversed, and a float position in which the rod and head ends of the cylinders are interconnected through a regeneration path which is provided with a restricted bleed connection through which the oil displaced by the .cylinder rods can escape to the tank. The power down position is used for digging, whereas the float position 3,477,347 Patented Nov. 11, 1969 interconnecting the cylinders and the valve frequently are long, and also because the valve itself normally is sized to handle the output of the supply pump and not the much greater fio'w rate required for rapid dropping of the bucket. Therefore, it should be evident that, in order to maintain the expanding ends of the cylinders liquid-filled, and thus preclude cavitation, it is necessary to establish a relatively high pressure at the directional control valve. This can be accomplished only by severely restricting the bleed connection through which the oil displaced by the cylinder rods escapes to tank, and this necessarily limits the maximum speed at which the boom can descend.

The second undesirable characteristic of the conventional circuit concerns its inability to provide adequate control over the speed of descent of the boom. During the bucket-dropping operation, the head ends of the cylinders are-contracted, so it is obvious that more oil will be displaced from these ends than can be absorbed by the expanding rod ends. The excess oil, which is the quantity displaced by the cylinder-rods, escapes to tank through the bleed connection established in the float position, and the rate at which this escape occurs determines the speed of descent. The directional control valve can be designed to provide a metering orifice in the bleed connection whose flow area is varied by manipulation of the valve. However, since this orifice necessarily is defined by relatively movable parts of the valve, and thus its characteristics are alfected by manufacturing tolerances, and the rate of flow through the bleed connection is relatively low, it is evident that the degree of flow metering which is provided is very limited. Therefore, as a practical matter, the operator has very little control over the speed of descent.

In an elfort to improve the performance of the conventional circuit, it has been proposed to transfer oil from the contracting to the expanding ends of the cylinders through a by-pass valve located at or near the cylinders. This approach is disclosed in U.S. Patent 3,033,168, granted May 8, 1962. In this arrangement, the bypass valve automatically opens whenever the directional control valve is shifted to float position and diverts directly to the rod ends of the cylinders all of the oil displaced from the head ends. The excess oil is returned to tank from the rod end side of the by-pass valve through the directional control valve. Since this scheme provides a very short regeneration flow path which completely bypasses the one created by the directional control valve, it obviously ellects a significant increase in bucket-dropping speed without incurring any greater'risk of cavitation in the rod ends of the cylinders. However, as in the conventional circuit, speed of descent can be controlled solely by throttling the flow to tank of the oil displaced by the cylinder rods and cannot be regulated with any real degree of precision.

SUMMARY OF INVENTION The object of this invention is to provide an improved regeneration scheme which alfords a high maximum speed of descent as well as good control over the speed of descent. In contrast to the prior circuits mentioned earlier, the new circuit provides'a pair of parallel regeneration paths through which oil is transferred from the contracting to the expanding ends of the cylinders. One of these paths extends through the directional control valve and contains a variable orifice whose flow area changes with movement of that valve within a range of floating positions. This path also is provided with a bleed connection containing a fixed orifice through which excess oil escapes to tank. The second regeneration path extends through a by-pass valve located at or near the cylinders, and it is automatically throttled by that valve as required to limit to a predetermined value the regenerative flow rate through the first path. The limiting fiow rate corresponds to the rating of the directional control valve, As the directional control valve is manipulated to increase and decrease the area of the variable orifice, the by-pass valve progressively opens and closes, respectively, to raise and lower the rate of flow through the second path. This, of course, changes the speed of descent. Since the variable orifice handles a substantially constant flow rate of a magnitude much greater than that attributable to cylinder rod displacement, it is evident that the improved circuit afiords better control over the speed of descent than either of the prior schemes described above. Moreover, since the circuit provides two parallel regeneration flow paths, and the rate of flow through the first is limited to a value which does not entail excessive pressure losses, it follows that the circuit provides a higher maximum speed of descent than the conventional circuit.

It also should be obserbed that, since the by-pass valve in the new circuit merely throttles the second regeneration path and does not perform the switching functions which characterize the by-pass valve of Patent 3,033,168, it can be relatively simple and inexpensive. In fact, experience shows that the cost of this component does not exceed greatly the two Ts which are used in the prior conventional circuit to connect the two actuating cylinders in parallel.

DESCRIPTION OF PREFERRED EMBODIMENT The preferred embodiment of the invention is described herein with reference to the accompanying drawing whose single figure is a schematic diagram of the complete power circuit.

Referring to the drawing, the improved circuit is employed to actuate a load 1 and includes a pair of doubleacting differential area power cylinders 2 and 3, a supply pump 4 and oil reservoir or tank 5, a four-position directional control valve 6, and a regenerative by-pass valve 7. The by-pass valve 7 is located at or near the cylinders 2 and 3 and serves to connect them in parallel across the main service lines 8 and 9 leading from the remotely located directional control valve 6; the head ends 2a and 3a of the cylinders being joined to main service line 9 via branch lines 1111 and 12a, and the rod ends 2b and 3b being joined to main service line 8 via branch lines 1112 and 12b.

Although in actual practice, pump 4 usually supplies several actuating circuits controlled by separate valve units in a common directional control valve, for convenience and clarity the illustrated valve 6 includes only the valve unit pertaining to the circuit of this invention, This valve unit comprises a valve bore 13 which contains a sliding, hollow valve plunger 14 and which is encircled by seven longitudinally spaced, annular chambers; there being a pair of supply chambers 14 and 15 which are connected with pump 4 through supply manifold 16, a pair of exhaust chambers 17 and 18 which are connected with tank through exhaust manifold 19, a center bypass chamber 21 which also leads to manifold 19, and a pair of motor chambers 22 and 23 connected, respectively, with main service lines 8 and '9. Valve plunger 14 is formed with a pair of center necks 24 and 25 which define three lands 26-28, and contains a pair of axial bores 29 and 31 through which oil is delivered to and from the motor chambers 22 and 23, respectively. The longer bore 29 is intersected by four sets of through radial passages 32-35, whereas bore 31 is intersected by only two sets of passages 36 and 37, which correspond to passages 32 and 33, and contains a conventional load drop check valve 38.

The valve plunger has the following four operating positions in which it establishes the connections indicated:

(1) A neutral position (N) in which lands 26 and 28 isolate motor chambers 22 and 23, respectively, from the other fluid-containing spaces of the valve, and center necks 24 and 25 connect by-pass chamber 21 with supply chambers 14 and 15, respectively, and thus complete an open center unloading path through valve 6.

(2) A raise position (R) in which lands 27 and 28 close the open center path, radial passages 37 and 36 register, respectively, with chambers 15 and 23, and radial passages 32, 33 and 35 register, respectively, with chambers 17, 22 and 21.

(3) A power down position (PD) in which lands 26 and 27 close the open center path, radial passages 32, 33 and 35 register, respectively, with chambers 22, 14 and 15, and radial passages 37 and 36 register, respectively, with chambers 23 and 18.

(4) A fioat position (F) in which center neck 24 interconnects chambers 15 and 21, radial passages 32 and 35 register, respectively, with motor chambers 22 and 23, radial passages 34 register with by-pass chamber 21, and radial passages 33 and 37 are closed by the wall of bore 13.

Each of the operative positions of valve plunger 14 actually includes a range of positions, and, therefore, as the plunger is shifted from neutral position to either the raise or power down position, it progressively throttles the open center path and meters flow to one or the other of the motor chambers 22 and 23. Similarly, when plunger 14 is in the float position, it can be manipulated to control the degree of registration between radial passages 35 and motor chamber 23. Thus, in this position, these passages serve as a variable area orifice in the regeneration path extending between motor chambers 22 and 23. The radial passages 34 also serve as a metering orifice in the float position, but in this case the flow area is fixed, and the orifice is in a bleed connection through which oil displaced by the cylinder rods 20 and 3c is delivered to tank 5. These passages 34 are so sized that the backpressure they create in bore 29 is adequate to force oil out to the expanding rod ends 2b and 3b of the cylinders.

By-pass valve 7 comprises a housing formed with three cored chambers 39, 41 and 42 which are provided with ports, only four of which are shown, through which they are connected with the lines 8, 9, 11a, 11b, 12a and 12b in the manner shown in the drawing, and which are spanned by a valve bore 43. This bore contains a reciprocable valve plunger 44 provided with a pair of necks 45 and 46 which define lands 4749. The bottom wall of neck 45 cooperates with the encircling housing land 51 to define an annular orifice 52 which has a fixed area and constitutes a continuously open flow connection between chambers 39 and 41. Valve plunger 44 is biased by a relatively low rate compression spring 53 to the illustrated closed position, in which land 48 prevents communication between chambers 41 and 42, and is shifted to the left to progressively open a regenerative flow path between these chambers by a pair of opposed pressure motors 54 and 55. These motors 54 and 55 are connected, respectively, with chambers 41 and 39 through the illustrated axial and radial passages formed in valve plunger 44, and therefore they open by-pass valve 7 as the rate of flow through orifice 52 in the direction of chamber 39 rises above a predetermined value. The flow area of orifice 52 is so correlated with the preload in spring 53 that this predetermined value corresponds approximately to the flow rating of directional control valve 6. Since spring 53 has a relatively low rate, it should be evident that valve 7 is effective to limit the regenerative flow rate through valve 6 to that rated value. The right edge of plunger land 48 is interrupted by a series of radial notches 56 formed by a drill bit and which serve to insure good flow-metering action.

When the improved circuit is in service and valve plunger 14 of directional control valve 6 is in the illustrated neutral position, lands 26 and 28 preclude flow into or out of motor chambers 22 and 23, so lay-pass valve 7 will assume its illustrated position, and cylinders 2 and 3 will be hydraulically locked. The oil delivered to valve 6 by pump 4 passes to tank 5 via supply manifold 16, chambers 14, and 21, and exhaust manifold 19, and therefore the pump will be unloaded.

When valve plunger 14 is shifted to the raise position (R), pump 4 is loaded, and oil under pressure is delivered to the head ends 2a and 3a of the cylinders via chamber 15, radial passages 37, bore 31, check valve 38, radial passages 36, chamber 23, main service line 9, chamber 39, orifice 52, chamber 41, and branch lines 11a and 12a. As the cylinders 2 and 3 lift load 1, the oil displaced from their rod ends 2b and 3b returns to tank 5 via branch lines 11b and 12b, chamber 42, "main service line 8, motor chamber 22, radial passages 33, bore 29, radial passages 32, chamber 17 and exhaust manifold 19. The direction of flow through orifice 52 is toward chamber 41, so motor 55 will be subjected to a higher pressure than motor 54, and by-pass valve 7 will be maintained closed. Since orifice 52 is sized to match the flow rating of valve 6, it will not create undue pressure losses in the supply path to the head ends 2a and 3a.

In order to force load 1 downward against an opposing external force, valve plunger 14 is shifted to the power down position. Under this condition, oil under pressure is delivered to rod ends 2b and 3b through a path comprising chambers 14 and 15, radial passages 33 and 35, bore 29, radial passages 32, motor chamber 22, line 8, chamber 42, and branch lines 11b and 12b, and the oil displaced from head ends 2a and 3a will return to tank 5 via branch lines 11a and 12a, chamber 41, orifice 52, chamber 39, line 9, motor chamber 23, radial passages 37, bore 31, check valve 38, radial passages 36, chamber 18 and exhaust manifold 19. Although oil now flows through orifice 52 from chamber 41 to chamber 38, and consequently motor 54 is subjected to a higher pressure than motor 55, by-pass valve 7 will not open because the rate of flow is limited by the capacity of pump 4 and always will be less than the value for which valve 7 is set.

When load 1 is in an elevated position from which it is to descend under the action of its own weight or an external force, valve plunger 14 is shifted to the float position. Now pump 4 is unloaded through the open center path provided by center neck 24, and the head ends 2a and 3a are connected with the rod ends 2b and 3b through a first regeneration path comprising branch lines 11a and 12a, chamber 41, orifice 52, chamber 39, main line 9, motor chamber 23, radial passages 35, axial bore 29, radial passages 32, motor chamber 22, main line 8, chamber 42 and branch lines 11b and 12b. Opening of this regeneration path allows load 1 to move downward and, as the rate of flow of oil through the'path increases, so too does the pressure drop across orifice 52. When the fiow rate reaches the value for which by-pass valve 7 is set, motors 54 and 55 shift valve plunger 44 to the left and open a parallel regeneration path through notches 56. As plunger 44 shifts, the flow restriction afforded by notches 56 decreases; consequently the rate of flow through the second regeneration path increases. Plunger 44 will come to rest in a position in which the flow rate through the second regeneration path is substantially equal to the difference between the rate at which load 1 currently is displacing oil from head ends 2a and 3a and the setting of valve 7. Of course, since the bias exerted by spring 53 varies with its deflection, the rate of flow through orifice 52 and the first regeneration path will increase slightly as valve 7 is opening.

Inasmuch as the head ends 2a and 3a of the cylinders have a greater effective area than the rod ends 2b and 3b, they will displace more oil than can be absorbed by the rod ends. The excess oil, which is equal to the volume swept by the cylinder rods 2c and 30, must be bled from the circuit in order for the cylinders to move, and. this function is performed by the restricted radial passages 34 in valve plunger 14. The degree of restriction afforded by these passages is such that the backpressure maintained in bore 29 will be adequate to maintain the rod ends 2b and 3b liquid-filled.

In the improved circuit, the rate of descent of load 1 is controlledby manipulating valve plunger 14 to vary the area of the orifice defined by radial passages 35. As the flow area of this orifice is increased, the rate of flow through the first regeneration path tends to increase.-

However, as it does so, the pressure drop across orifice 52 increases, and .motors 54 and 55 shift valve plunger 44 further to the left. This, of course, increases the rate of flow through notches 56. Since the rate at which oil 18 transferred from head ends 2a and 3a to rod ends 2b and 3b has increased, it follows the speed of descent of load 1 will increase. When plunger 14 is shifted in the direction to decrease the flow area of radial passages 35, the pressure differential across orifice 52 tends to decrease, spring 53 shifts valve plunger 44 to the right to throttle flow through notches 56, and the speed of descent of load 1 decreases.

During these speed-controlling operations, the throttling action of by-pass valve 7 tends to minimize changes in the flow rate through the first regeneration path. Therefore, from a practical standpoint, the fiow rate through this path is constant. This is important because it insures that, throughout the controlling range of valve 7, radial passages 35 will handle the flow rate needed for reasonably good metering action. As a result, the operator will be able to regulate rather closely the speed of descent of oad 1.

Although most installations of the type under discussion employ differential area cylinders, it should be realized that the improved regeneration scheme can be used with cylinders of the equal area type. In this case, however, the bleed connection provided by restricted passages 34 must be eliminated.

I claim:

1. In combination (a) a double-acting cylinder (2) including a piston and opposed chamber ends (2a and 2b) and arranged to actuate a load (1) which tends to contract one (2a) of said chamber ends;

(b) a first regeneration path containing a by-pass valve (7) and connected with the two ends of the cylinder;

(c) directional control valve means (6) connected with the chamber ends of the cylinder through service connections (8, 9, 11a, 11b) and having a range of positions in which it provides a second regeneration path (29, 32, 35) interconnecting said service connections and containing a flow restrictor (35) whose area varies with movement of the valve means; and

(d) actuating means (52-55) responsive to the rate of flow from said one chamber end (2a) to said second regeneration path through the associated service connection (111:, 9) when the directional control valve means (6) is in said range of positions for opening the bypass valve as needed to limit said rate of flow while said second regeneration path remains open.

2. The combination defined in claim 1 wherein the actuating means comprises (a) a reference orifice (52) in said associated service connection (9, 11a); and

(b) fluid pressure motor means (53-55) that positions the by-pass valve (7 in accordance with the pressure differential across the reference orifice.

3. The combination defined in claim 2 wherein the fluid pressure motor means comprises (a) a spring (53) biasing the by-pass valve (7 in the closing direction; and

7 8 (b) a pair of opposed fluid pressure motors (54, 55) References Cited {gr shitting the lgyt-lpass vtalve (zggsingt the agltgarns og UNITED STATES PATENTS e s rm one o e mo ors emg re 1 to th prissure at the cylinder side of the reference 2,916,050 12/1959 Ruhl 137-62558 orifice (52) and urging the valve (7) open and the 5 21949997 8/1960 Vander Kaay 91437 X other motor (55) being responsive to the pressure at 3'O33'168 5/1962 Ruhl 91-438 X the opposite side of the reference orifice. 3,313,316 4/1967 Thomas 91-437 X 4. The combination defined in claim 1 wherein 3'335'739 8/1967 Rlce 91-437 X (alrglletgglhien-gctmg cylinder (2) 1s of the driferentlal M ARTIN P. SCHWADRON, Primary Examiner (b) the directional control valve means (6) provides I. C. COHEN. Assistant Examiner a bleed connection (34) having a fixed flow area U S Cl XR leading from the second regeneration path (29, 32, 

